in CvDTreeTrainData::subsample_data [[CvDTreeTrainData]]::subsample_data in mltree.cpp, the modification should be made as following by comment the first one and add the second one. After fix the bug in weight_trimming. The difference is not to use the function in the derived class (such as the CvCascadeBoostTrainData) [[CvCascadeBoostTrainData]])

//const int* src = get_cat_var_data( data_root, vi, (int*)(uchar*)inn_buf );
const int* src = CvDTreeTrainData::get_cat_var_data( [[CvDTreeTrainData]]::get_cat_var_data( data_root, vi, (int*)(uchar*)inn_buf );